A long cylindrical conductor of radius 'a' has a long cylindrical hole of radius 'b'.The axis of the hole is parallel to the axis of the conductor. A current 'i' is uniformly spread in the conductor. Show that the magnetic frield at the centerof the hole is given by
B= [{meu_knot}*i*d]/[2*pi*(a^2 - b^2)]
I am flummoxed.
